Decoupling capacitor and method of making same

ABSTRACT

A semiconductor substrate has at least two active regions, each having at least one active device that includes a gate electrode layer, and a shallow trench isolation (STI) region between the active regions. A decoupling capacitor comprises first and second dummy conductive patterns formed in the same gate electrode layer over the STI region. The first and second dummy conductive regions are unconnected to any of the at least one active device. The first dummy conductive pattern is connected to a source of a first potential. The second dummy conductive pattern is connected to a source of a second potential. A dielectric material is provided between the first and second dummy conductive patterns.

This application is a division of U.S. patent application Ser. No.13/344,137, filed Jan. 5, 2012, which is expressly incorporated byreference herein in its entirety.

FIELD

This disclosure relates to semiconductor integrated circuit devices andfabrication methods.

BACKGROUND

Power supply lines in a semiconductor integrated circuit (IC) supplycurrent to charge and discharge active and passive devices in the IC.For example, digital complementary metal-oxide-semiconductor (CMOS)circuits draw current when the clock makes a transition. During theoperation of circuits, the power supply lines supply transient currentswith a relatively high intensity, which can result in voltage noise onthe power supply lines. The voltage on the power supply line willfluctuate when the fluctuation time of the transient current is short orwhen its parasitic inductance or parasitic resistance is large.

The operational frequency of the IC may be on the order of severalhundreds of mega-hertz (MHz) to several giga-hertz (GHz). In suchcircuits, the rising time of clock signals is very short, so thatvoltage fluctuations in the supply line may be very large. Undesiredvoltage fluctuations in the power supply line powering a circuit cancause noise on its internal signals and degrade noise margins. Thedegradation of noise margins can reduce circuit reliability or evencause circuit malfunction.

To reduce the magnitude of voltage fluctuations in the power supplylines, filtering or decoupling capacitors are usually used between theterminals of different power supply lines or between terminals of powersupply line and the ground line. Decoupling capacitors act as chargereservoirs that additionally supply currents to circuits to preventmomentary drops in supply voltage.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic plan view of a portion of an IC having adecoupling capacitor between metal oxide semiconductor field effecttransistors (MOSFETs).

FIG. 2 is a side elevation cross sectional view of the device of FIG. 1,taken along section line 2-2 of FIG. 1.

FIG. 3 is a schematic plan view of a portion of an IC having adecoupling capacitor between bipolar junction transistors (BJT).

FIG. 4 is a block diagram of a computer system for providing an EDA toolthat uses a cell library for forming the decoupling capacitor.

FIG. 5 is a schematic plan view of a portion of an IC having additionaldecoupling capacitance between metal oxide semiconductor field effecttransistors (MOSFETs).

DETAILED DESCRIPTION

This description of the exemplary embodiments is intended to be read inconnection with the accompanying drawings, which are to be consideredpart of the entire written description. In the description, relativeterms such as “lower,” “upper,” “horizontal,” “vertical,”, “above,”“below,” “up,” “down,” “top” and “bottom” as well as derivative thereof(e.g., “horizontally,” “downwardly,” “upwardly,” etc.) should beconstrued to refer to the orientation as then described or as shown inthe drawing under discussion. These relative terms are for convenienceof description and do not require that the apparatus be constructed oroperated in a particular orientation. Terms concerning attachments,coupling and the like, such as “connected” and “interconnected,” referto a relationship wherein structures are secured or attached to oneanother either directly or indirectly through intervening structures, aswell as both movable or rigid attachments or relationships, unlessexpressly described otherwise.

For advanced technologies, such as those having critical dimensions (CD)of 32 nm or smaller, stricter design rules may be adopted to promotehigh yield. One design rule that is frequently employed is the use of a“poly-density” rule. “Poly-density” refers to the ratio of the area ofgate electrode layer material to the total IC area. It has beendetermined that maintaining at least a minimum threshold poly-densityacross the IC helps prevent dishing and erosion in subsequentlydeposited interconnect layers.

Poly-density design rules are observed regardless of whether the gateelectrode layer is formed of polycrystalline silicon or a high-k metalgate material. In the description below, unless expressly indicated torefer to semiconductor, references to “poly layer material” refers toany gate electrode layer material, regardless of whether polycrystallinesilicon or metal.

In many cases, the area occupied by gate and/or capacitor electrodes inthe gate electrode layer is relatively small compared to an area thatmeets the poly-density design rule. To meet the design rule, dummy polylayer material is inserted. The dummy poly layer material is not partof, or connected to, any of the active devices of the IC, and does notperform any logic function. Dummy poly layer patterns may be located onthe shallow trench isolation (STI) region next to the active area, forexample. Addition of dummy poly layer material to meet the poly densitydesign rule can help poly gate lithography, and also help edgefinger-configuration source/drain (S/D) regions avoid abnormal epitaxialmaterial formation. Dummy poly patterns may be placed over the STIregions for either analog or digital circuits.

Embodiments described below utilize dummy poly patterns on STI to formmetal-oxide-metal (MOM) decoupling capacitors between active devices.Thus, the dummy patterns serve a dual purpose. In addition to satisfyingpoly density design rules, the dummy patterns form fringe-typedecoupling capacitors. If a design already includes dummy conductorpatterns, there is no need to occupy a large chip area with additionaldecoupling capacitor patterns, and vice-versa.

FIGS. 1 and 2 show one example of an IC 100 having a decouplingcapacitor structure 135.

The IC includes semiconductor substrate 103. The substrate 103 can be asilicon substrate, a III-V compound substrate, a silicon/germanium(SiGe) substrate, a silicon-on-insulator (SOI) substrate, a displaysubstrate such as a liquid crystal display (LCD), a plasma display, anelectro luminescence (EL) lamp display, or a light emitting diode (LED)substrate, for example. In some embodiments, at least one transistor115, diode, device, circuit or other semiconductor structure or variouscombinations thereof (not shown) are formed below the dielectric layer170 and electrically coupled to each other. Although FIGS. 1 and 2 showtransistors 115, the decoupling capacitors 135 and 136 may be configuredand used similarly for diodes or other devices.

FIG. 2 shows the configuration at the conclusion of front end of line(FEOL) processing, up to the first metal layer (M1) 165. One of ordinaryskill in the art understands that additional interconnect layers aresubsequently formed during back end of line (BEOL) processing. Theseadditional BEOL layers are omitted from FIGS. 1 and 2 for clarity. Also,although FIGS. 1 and 2 show interconnections in the M1 layer connectingthe dummy conductor 130 to the VDD bus 140 and connecting dummyconductor 131 to the VSS bus 141, one of ordinary skill can readily formsimilar connections in the M2, M3 or other interconnect layer.

FIG. 2 shows a cross section of the P MOSFETs 115. The IC includes atleast two active regions 110, each having at least one active device 115that includes a gate electrode layer 120. A shallow trench isolation(STI) region 105 is provided between the active regions 110, Each PMOS115 has an N well 101, with the N wells separated by a STI region 105. Apair of source/drain regions 110 are formed in the substrate byimplanting P+ impurities (e.g., boron). Each N MOSFET 116 has a P wellwith source drain regions 110 formed by implanting N+ impurities (e.g.,phosphorus).

A thin gate insulating layer (not shown) is formed between and above thesource/drain regions 110. In some embodiments, a silicon oxide gateinsulating layer is provided. In other embodiments, the insulating layercomprises a high-K dielectric, such as, but not limited to, a hafniumbased oxide, a hafnium based oxynitride, or a hafnium-siliconoxynitride, hafnium silicate, zirconium silicate, hafnium dioxide andzirconium dioxide. The high-k dielectric layer may include a binary orternary high-k film such as HfO, LaO, AlO, ZrO, TiO, Ta2O5, Y2O3, STO,BTO, BaZrO, HfZrO, HfLaO, HfTaO, HfTiO, combinations thereof, or othersuitable materials. Alternatively, the high-k dielectric layer 111 mayoptionally include a silicate such as HfSiO, LaSiO, AlSiO, combinationsthereof. The insulating layer may be deposited using atomic layerdeposition.

Gate electrodes 120 are then formed between and above the source/drainregions 110, above the gate insulating layer. The gate electrode 120 maycomprise polycrystalline silicon, or a metal or alloy, such as but notlimited to, titanium nitride, tantalum nitride, or aluminum nitride.

At the same time the gate electrodes 120 are formed, the dummy conductorpatterns 130, 131 are formed in the same gate electrode layer, over theSTI regions 105. The dummy conductors 130, 131 can be convenientlypatterned using the same photomask that patterns the gate electrodes120, without adding any step or photomask to the fabrication process. Insome embodiments, the dummy conductor patterns 130, 131 are elongatedline segments.

Dielectric material 170 fills the space between the dummy conductors130, 131. The dielectric material 170 may include one or more layers ofsame or different dielectric materials. For example, dielectric 170 mayinclude two layers formed sequentially above the substrate 103 and gateelectrodes 120. These two layers may include: a passivation layer (notshown) such as silicon nitride (SiN) or silicon carbon nitride and adielectric layer (not shown) such as silicon oxynitride or a low-kdielectric material having a dielectric constant of about 3.5 or less,such as “SiLK™” dielectric from Dow Chemical Co. of Midland Mich., or“Black Diamond™” dielectric from Applied Materials Corp. of Santa Clara,Calif.

Each adjacent pair of dummy conductor patterns 130, 131 and thedielectric material 170 between them forms a decoupling capacitor 135,shown schematically in FIGS. 1 and 2. The decoupling capacitor 135 isprovided by the fringe capacitance between the side edges of conductors130 and 131, which face each other. Thus, the capacitance of thedecoupling capacitor 135 depends on the thickness of the gate electrodelayer 130, 131, the length of the overlapping portions of the dummyconductors 130, 131, the distance between the adjacent edges ofconductors 130, 131 and the dielectric constant of the dielectricmaterial 170. Each decoupling capacitor has a length L that is greaterthan a width W of the active region 110. In some embodiments, the firstand second conductive patterns extend nearly the entire distance betweenthe VDD bus and the VSS bus, maximizing the decoupling capacitance. Eachgate electrode has a gate width GW, and the first and second dummyconductive patterns 130, 131 are each longer than the gate width GW.

Contact vias 150 are formed for interconnecting the source/drain regions110 in the interconnect layers. Contact vias 150 are also formed at oneend of each of the dummy conductors 130, 131. In some embodiments, thecontact vias are arranged so that contact vias 150 for conductors 130are at the end of the conductors closer to the VDD bus 140, and contactvias 150 for conductors 131 are at the end of the conductors closer tothe VSS bus 141. For forming the contacts, contact openings are formedin the dielectric 170, and a metal such as tungsten is deposited viasputter deposition, evaporation or chemical vapor deposition (CVD).

As shown in FIG. 1, a power (VDD) bus 140 and a ground (VSS) bus 141 areprovided in the M1 layer. Line segments 165 in the M1 layer connects thecontact via 150 of dummy conductor 130 to the power bus 140 and connectsthe contact via 150 of dummy conductor 131 to the ground bus 141. Thus,the first dummy conductive pattern 130 is connected to a source of afirst potential, and the second dummy conductive pattern connected to asource of a second potential.

FIG. 3 shows another example of an IC 200, in which the at least oneactive device is a bipolar junction transistor (BJT) 215. BJT 215includes three differently doped semiconductor regions, the emitter 220,the base region 221 and the collector region 222. In some embodiments,the emitter 220, base 221 and collector 222 regions are p type, n typeand p type, respectively forming a PNP transistor. In other embodiments,the emitter, base and collector regions are n type, p type and n type,forming an NPN transistor. The emitter region 220 may be formed in thepolysilicon layer. The emitter region of the polysilicon layer 220 isimplanted (or doped in-situ) with boron or another p-type dopant for aPNP transistor, or implanted with arsenic or another n-type dopant foran NPN transistor.

At the same time the emitter 220 is formed, the dummy conductor patterns130, 131 are formed in the same polysilicon layer, over the STI regions105. The dummy conductors 130, 131 can be conveniently patterned usingthe same photomask that patterns the emitter 220, without adding anystep or photomask to the fabrication process. In some embodiments, thedummy conductor patterns 130, 131 are elongated line segments.

Dielectric material 170 fills the space between the dummy conductors130, 131. The dielectric material 170 may include one or more layers ofsame or different dielectric materials. For example, dielectric 170 mayinclude any of the dielectric materials described above with referenceto the embodiment of FIGS. 1 and 2.

Each adjacent pair of dummy conductor patterns 130, 131 and thedielectric material 170 between them forms a decoupling capacitor 135,shown schematically in FIG. 3. The decoupling capacitor 135 is providedby the fringe capacitance between the side edges of conductors 130 and131, which face each other.

Although examples are described above using the dummy conductivepatterns in the poly layer to form decoupling capacitors between MOSFETsin an NMOS, PMOS or CMOS process, or between BJTs in a bipolar process,the same decoupling capacitors may be used between MOSFETs and BJTs in aBiCMOS process. In a BiCMOS process, the same polysilicon layer canprovide gate electrodes, dummy conductors and decoupling capacitors inthe MOSFETs, and emitter regions, dummy conductors and decouplingcapacitors for the BJTs.

FIG. 4 shows a modification to a standard cell library to incorporatethe decoupling capacitors described above. Herein, the term “standardcell” refers to the cells' attribute of being a selectable, reusableunit to be used with an electronic design automation (EDA) tool, anddoes not imply any limitation as to whether the cell designs areconventional or future developed cells. A programmed processor 420 isconfigured to operate an EDA tool 422. The processor 420 may be, forexample, a general purpose computer or embedded processor configured byprogramming with special purpose computer program instructions 416stored in a persistent machine readable storage medium 412. The EDA tool422 may include, for example, tools for logic synthesis, place androute, design rule checks and layout versus schematic, among others. Themedium also includes other data 414, including but not limited to designrule data.

For example, an EDA tool may use a combination of the following modules:logic synthesis, behavioral synthesis, place and route, static timinganalysis, formal verification, HDL (SystemC, Systemverilog/Verilog,VHDL) simulators as well as transistor-level circuit simulation. Suchsystems may include a physical implementation/verification tool, e.g.,IC Compiler, or ICValidator Synopsys of Mountain View, Calif., CadenceSystem Development Suite (e.g.,: SoC Encounter, Cadence PhysicalVerification System) by Cadence Design Systems, Inc. of San Jose,Calif., and “CALIBRE® INROUTE” by Mentor Graphics of Wilsonville, Oreg.

The persistent, computer readable storage medium 412 is encoded with anintegrated circuit (IC) cell library 400. The cell library 400 includesa plurality of cells including, but not limited to the cells 402, 404,406, 408, 410 shown. Many other types of cells are known to those ofordinary skill in the art and are not described herein for brevity. Eachcell includes data that configure an electronic design automation tool422 to generate a layout of an IC component.

The cell library may include one or more standard cells for each ofMOSFETs 402 and BTJs 406. In some embodiments, a cell 410 is providedfor forming a decoupling capacitor using fringe capacitance of a pair ofdummy conductors 130, 131 in the same poly layer as each other, over anSTI region 105.

In some embodiments, one or more cells are provided for defining atransistor having at least one decoupling capacitor adjacent to it. Insome embodiments, the cell defines a semiconductor substrate 103 having:at least one active region, having at least one active device 115, 215that includes a polysilicon layer 120, 220, and a shallow trenchisolation (STI) region 105 adjacent the active region, and a decouplingcapacitor 135. If the cell is a MOSFET, the polysilicon layer is thegate electrode layer. If the cell is a BJT, the polysilicon layer is theemitter layer. The decoupling capacitor comprises first and second dummyconductive patterns 130, 131 formed in the same polysilicon layer 120over the STI region 105. The first and second dummy conductive regions130, 131 are unconnected to any of the at least one active device. Thefirst dummy conductive pattern 130 is connected to a source of a firstpotential, and the second dummy conductive pattern connected to a sourceof a second potential. A dielectric material between the first andsecond dummy conductive patterns. The first dummy conductive pattern 130is connected to a power bus in a conductive line layer by way of a firstcontact via, and the second dummy conductive pattern 131 is connected toa ground bus in the conductive line layer by way of a second contactvia. The first and second dummy conductive patterns 130, 131 are sizedso that a polysilicon density of the IC is greater than or equal to atarget polysilicon density.

FIG. 5 shows a MOSFET embodiment similar to the embodiment of FIG. 1,with optional additional decoupling capacitance. Instead of using squareor round contacts 150 for the source/drain regions 110, elongated slotcontacts 550 are provided on the source/drain implant regions. Theelongated slot contacts 550 provide an additional decoupling capacitancebetween the source/drain slot contact and the adjacent dummy conductor.

Examples are described above in which decoupling capacitances are addedbetween adjacent transistors. In other embodiments, the decouplingcapacitors may be located between other types of devices, such as, butnot limited to, active area resistors and diodes.

The decoupling capacitors described herein may be used in combinationwith a variety of functional circuit elements, including digital and/oranalog circuits.

By providing decoupling capacitors using dummy conductors that arealready to be included in the layout, the structure and method describedherein can save substantial area in the IC, which may be used to addother functions or redundant cells. For some designs, the area savingsmay be about 4.5%.

In some embodiments, a structure comprises a semiconductor substratehaving at least two active regions, each having at least one activedevice that includes a gate electrode layer, and a shallow trenchisolation (STI) region between the active regions. A decouplingcapacitor comprises first and second dummy conductive patterns formed inthe same gate electrode layer over the STI region. The first and seconddummy conductive regions are unconnected to any of the at least oneactive device. The first dummy conductive pattern is connected to asource of a first potential. The second dummy conductive pattern isconnected to a source of a second potential. A dielectric material isprovided between the first and second dummy conductive patterns.

In some embodiments, a structure comprises a semiconductor substratehaving at least two active regions, and a shallow trench isolation (STI)region between the active regions. Each active region has at least oneactive device that includes a polysilicon layer. A decoupling capacitorcomprises first and second dummy conductive patterns formed in the samepolysilicon layer over the STI region. The first and second dummyconductive regions are unconnected to any of the at least one activedevice. The first dummy conductive pattern is connected to a source of afirst potential. The second dummy conductive pattern is connected to asource of a second potential. A dielectric material is provided betweenthe first and second dummy conductive patterns.

In some embodiments, a method comprises: (a) providing a semiconductorsubstrate having at least two active regions, and a shallow trenchisolation (STI) region between the active regions; (b) forming a singlegate electrode layer above the substrate, the gate electrode layerhaving: at least one gate electrode above each of the at least twoactive regions, and first and second dummy conductive patterns above theSTI region, the first and second dummy conductive regions beingunconnected to any of the at least one active device, the first dummyconductive pattern to be connected to a source of a first potential, thesecond dummy conductive pattern to be connected to a source of a secondpotential; and (c) providing a dielectric material between the first andsecond dummy conductive patterns, thereby to form a decouplingcapacitor.

Although the subject matter has been described in terms of exemplaryembodiments, it is not limited thereto. Rather, the appended claimsshould be construed broadly, to include other variants and embodiments,which may be made by those skilled in the art.

What is claimed is:
 1. A structure comprising: a semiconductor substratehaving: at least two bipolar junction transistors (BJT), each includingan emitter layer, and a shallow trench isolation (STI) region betweenthe BJTs; and a capacitor comprising: first and second dummy conductivepatterns formed in the emitter layer and over the STI region, the firstdummy conductive pattern configured to be connected to a source of afirst potential, the second dummy conductive pattern configured to beconnected to a source of a second potential; and a dielectric materialbetween the first and second dummy conductive patterns.
 2. The structureof claim 1, wherein the first and second dummy conductive regions areunconnected to any of the at least two BJT.
 3. The structure of claim 1,wherein the capacitor is a decoupling capacitor.
 4. The structure ofclaim 1, wherein the substrate comprises a first active regioncontaining the first BJT, a second active region containing the secondBJT, and a third active region between the first active region and aground bus.
 5. The structure of claim 4, wherein each of the first andsecond conductive patterns extends nearly a distance between a power busand the ground bus.
 6. The structure of claim 1, wherein the first dummyconductive pattern is connected to power, and the second dummyconductive pattern is connected to a ground.
 7. The structure of claim1, wherein the first and second dummy conductive patterns are linesegments, each having a length that is greater than a length of anemitter of each BJT.
 8. The structure of claim 1, wherein the first andsecond dummy conductive patterns are formed of polycrystalline silicon.9. A structure comprising: a semiconductor substrate having: at leasttwo bipolar junction transistors (BJT) that includes a polysilicon layerin which an emitter is formed, and a shallow trench isolation (STI)region between the at least two BJT, and first and second conductivepatterns formed in the polysilicon layer over the STI region, the firstand second conductive patterns being unconnected to any of the at leasttwo BJT, the first conductive pattern configured to be connected to asource of a first potential, the second conductive pattern configured tobe connected to a source of a second potential.
 10. The structure ofclaim 9, further comprising a dielectric material between the first andsecond conductive patterns.
 11. The structure of claim 9, wherein thefirst and second conductive patterns are dummy patterns.
 12. Thestructure of claim 9, wherein the first and second conductive regionsare included in a decoupling capacitor.
 13. The structure of claim 9,wherein the polysilicon layer is doped in the emitter region.
 14. Amethod comprising: providing a semiconductor substrate having at leasttwo active regions, and a shallow trench isolation (STI) region betweenthe active regions; forming a single gate electrode layer above thesubstrate, the gate electrode layer having: at least one gate electrodeabove each of the at least two active regions, and first and secondconductive patterns above the STI region, the first and secondconductive patterns being located between the active regions andunconnected to any of the active regions, the first conductive patternto be connected to a source of a first potential, the second conductivepattern to be connected to a source of a second potential; wherein theSTI region below the first and second conductive patterns borders theactive regions.
 15. The method of claim 14, further comprising providinga dielectric material between the first and second conductive patterns,thereby to form a decoupling capacitor.
 16. The method of claim 14,wherein the first and second conductive patterns are dummy patterns. 17.The method of claim 14, further comprising connecting the firstconductive pattern to a VDD bus in a conductive line layer by way of afirst contact via, and the second conductive pattern is connected to aVSS bus in the conductive line layer by way of a second contact via. 18.The method of claim 14, wherein the first and second conductive patternsare line segments, each having a length that is greater than a width ofthe active region.
 19. The method of claim 14, wherein: each activeregion has at least one gate electrode, each gate electrode has a gatewidth, and the first and second conductive patterns are each longer thanthe gate width.
 20. The method of claim 14, wherein the first and secondconductive patterns are formed of polycrystalline silicon or a metalgate material.